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Valves in safety applications

03.01.2002  |  Goble, W.,  exida LLC, Sellersville, Pennsylvania


As the safety lifecycle (SLC) methods of ISA84.01 and IEC61508 are becoming more widespread, engineers who design safety instrumented systems (SISs) are starting to think more about the valves they use. Remember that the standards use a quantitative approach to safety verification for the hardware. A given set of equipment intended to protect against a specific hazard (a safety instrumented function, SIF) has a requirement to achieve a certain risk-reduction factor. This is established during risk analysis and stated in the safety requirements specification. Failure rates and modes of the various pieces of equipment are input to a reliability and safety analysis model that results in calculating the achieved risk reduction factor, RRF, probability of failure on demand average, PFDavg, safe failure fraction, SFF, and other metrics. The results achieved must meet or exceed the requirements.

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